Method for making mesoporous magnesium hydroxide nanoplates, an antibacterial composition, and a method of reducing nitroaromatic compounds

ABSTRACT

A method for producing mesoporous magnesium hydroxide nanoplates involving solvothermal treatment of a solution of a magnesium salt, a base, a glycol, and water is disclosed. The method does not use a surfactant or template in the solvothermal treatment. The method yields mesoporous nanoparticles of magnesium hydroxide having a plate-like morphology with a diameter of 20 nm to 100 nm, a mean pore diameter of 2 to 10 nm, a surface area of 50 to 70 m 2 /g, and a type-III nitrogen adsorption-desorption BET isotherm with a H3 hysteresis loop. An antibacterial composition containing the mesoporous magnesium hydroxide nanoplates is also disclosed. A method for reducing nitroaromatic compounds with a reducing agent and the mesoporous magnesium hydroxide nanoplates as a catalyst is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication. No. 62/842,069 filed on May 2, 2019, the entire contents ofwhich are herein incorporated by reference.

STATEMENT OF ACKNOWLEDGEMENT

The inventors acknowledge the support provided by the Deanship ofScientific Research (DSR) King Fand University of Petroleum and Minerals(KFUPM), Kingdom of Saudi Arabia, through funding this work (Project No.SR161009).

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates a method of preparing mesoporous magnesiumhydroxide nanoplates, an antibacterial composition containing themesoporous magnesium hydroxide nanoplates, and a method of reducingnitroaromatic compounds using the nanoplates.

Discussion of the Background

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

The synthesis of nanomaterials with particular morphologies is ofinterest because different morphologies can provide differentproperties. Various reported morphologies include rods [J. Xu, P. Gao,T. Zhao, Energy Environ. Sci. 2012, 5, 5333], sea-urchins [Y. H. Su, W.H. Lai, W. Y. Chen, M. H. Hon, S. H. Chang, Appl. Phys. Lett. 2007, 90,181905], flowers [S. Mourdikoudis, T. Altantzis, L. M. Liz-Marziin, S.Bals,I. Pastoriza Santos, J. Perez-Juste, CrystEngComm 2016, 18, 3422;and P. S. Das, A. Dey, A. K. Mandel, N. Dey, A. K. Mukhopadhyay, J.Adv.Ceram. 2013, 2, 173], plates [J. C. Yu, A. Xu, L. Zhang, R. Song, L.Wu, J. Phys. Chem. B. 2004,108, 64], and spheres [L. Ge, X. Jing, J.Wang, S. Jamil, Q. Liu, D. Song, J. Wang, Y. Xie,P. Yang, M. L. Zhang,Cryst. Growth Des. 2010,10, just to name a few. Magnesium is a cheapalkaline earth metal and magnesium nanoscale compounds are largely usedin biomedicine [S. Li, X. L. Qiao, J. G. Chen, C. L. Wu, B. Mei, J.Funct. Mater. 2005,11, 001; and J. Zhao, X Zhang, R. Tu, C. Lu, X He, W.Zhang, Cellulose 2014, 21,1859], adsorption [V. Srivastava, Y. Sharma,M. Sillanpaa, Ceram Int. 2015, 41, 6702], ceramics [M. Morales, J.Formosa, E. Xuriguera, M. Niubo, M. Segarra, J. Chimenos, Ceram. Int.2015, 41, 12137], devices [S. Wu, H. Wang, J. Sun, F. Song, Z. Wang, M.Yang, H. Xi, Y. Xie, H. Gao, J. Ma, X Ma, Y. Hao, IEEE Electron DeviceLett. 2016, 37, 990], sensors [S. Shukla, G. Parashar, A. Mishra, P.Misra, B. Yadav, R. Shukla, L. Bali, G. Dubey, Sens. Actuators, B 2004,98, 5.], and catalysts [M. Shaikh, M. Sahu, P. K. Gavel, G. R. Turpu, S.Khilari, D. Pradhan, K. V. S. Ranganath, Catal. Commun. 2016, 84, 89].

Various morphologies and applications of magnesium hydroxide (Mg(OH)₂)have been reported: for example, their electronic and optical propertiesdue to their small size and high crystallinity. Its nanoneedles andnanolamellas are good reinforcing materials. Mg(OH)₂ nanorods act asgood catalyzing agents in polymer composites [J. Lv, L. Qiu, B. Qu,Nanotechnology 2004, 15, 1576]. Its nano-forms are largely used asfillers in flame retardant composites because they can undergoendothermic reaction while under the influence of fire. Moreover,Mg(OH)₂ is used as a precursor for the synthesis of magnesium oxidenanomaterials. Therefore, morphology-controlled and high yield synthesisof Mg(OH)₂ nanomaterial is desirable.

Sol-gel techniques [R. Giorgi, C. Bozzi, L. Dei, C. Gabbiani, B. W.Ninham, P. Baglioni, Langmuir 2005, 21, 8495],microwave/ultrasound-assisted techniques [G. W. Beall, E. S. M. Duraia,F. El-Tantawy, F. Al-Hazmi, A. A. A1-Ghamdi, Powder Technol. 2013, 234,26; and O. Baidukova, E. V. Skorb, Ultrason. Sonochem. 2016, 31, 423],the precipitation of a magnesium salt with an alkaline solution [W.Jiang, X Hua, Q. Han, X Yang, L. Lu, X Wang, Powder Technol. 2009, 191,227], and solvothermal treatment [Y. Chen, T. Thou, H. Fang, S. Li, Y.Yao, Y. He, Procedia Eng. 2015, 102, 388; and L. Kumari, W. Z. Li, C. H.Vannoy, R. M. Leblanc, D. Z. Wang, Ceram. Int. 2009, 35, 3355] arecommonly used for the synthesis of Mg(OH)₂ nanomaterials. Among thesemethods, solvothermal treatment is most advantageous with respect to thesynthesis of well-defined and morphology-controlled products. Ding etal. have reported the synthesis of nanorod, nanotube, nanoneedle, andnanolamella morphologies of Mg(OH)₂ by the solvothermal approach [Y.Ding, G. Zhang, H. Wu, B. Hai, L. Wang, Y. Qian, Chem. Mater. 2001, 13,435]. Yu et al. have reported the synthesis of porous Mg(OH)₂ nanoplatesby a hydrothermal method P. C. Yu, A. Xu, L. Zhang, R. Song, L. Wu, J.Phys. Chem. B. 2004, 108, 64]. Fan et al. have reported the synthesis ofnanowires of Mg(OH)₂ by the solvothermal approach [W. Fan, X. Song, S.Sun, X Zhao, J. Cryst. Growth 2007, 305, 167]. Zhao et al. have reportedthe synthesis and antibacterial activity of irregular Mg(OH)₂nanoplatelets. Their reported nanoplatelets were of large size and hadirregular morphology. The structure of those nanoplatelets was notporous [J. Zhao, X. Zhang, R.. Tu, C. Lu, X. He, W. Zhang, Cellulose2014, 21, 1859]. The synthesis of very thin walled and porous Mg(OH)₂nanoplatelets without the use of any surfactant or template has not beenreported. Moreover, the antibacterial and catalytic applications of thenanoplatelets have not been studied previously.

In view of the foregoing, one objective of this disclosure is to providemethods of synthesizing mesoporous Mg(OH)₂ nanoplates by thesolvothermal method without the use of a surfactant or template.

SUMMARY OF THE INVENTION

The present disclosure relates to a method for making mesoporousmagnesium hydroxide nanoplates with a diameter of 20 nm to 100 nm,involving solvothermal treatment of aqueous mixture of a magnesium salt,a base, and a glycol having 2 to 6 carbon atoms at a temperature of 140to 220° C. for 1 to 24 hours, wherein the aqueous mixture issubstantially free of a surfactant, a template, or both.

In some embodiments, the magnesium salt is a magnesium halide.

In preferred embodiments, the magnesium halide is magnesium chloride.

In some embodiments, the magnesium salt is present in the aqueousmixture in an amount of 15 to 25 g/L.

In preferred embodiments, the base is a monoacidic base.

In preferred embodiments, the base is an acetate base.

In preferred embodiments, the base is sodium acetate.

In preferred embodiments, the base is present in the aqueous mixture inan amount of 25 to 40 g/L.

In some embodiments, the mole ratio of the amount of base present in theaqueous mixture to the amount of magnesium present in the aqueousmixture 1:1 to 3:1.

In preferred embodiments, the glycol is ethylene glycol.

In preferred embodiments, the glycol is present in the aqueous mixturein an amount of 15 to 25 volume %, based on a total volume of theaqueous mixture.

In some embodiments, the aqueous mixture is formed by mixing themagnesium salt and the base in water for 1 to 30 minutes, followed bythe addition of the glycol.

In some embodiments, after the addition of the glycol, the aqueousmixture is mixed for 1 to 30 minutes before the heating.

In some embodiments, the mesoporous magnesium hydroxide nanoplates havea mean pore diameter of 2 to 10 nm, a surface area of 50 to 70 m²/g, anda type-III nitrogen adsorption-desorption BET isotherm with a H3hysteresis loop.

In preferred embodiments, the mesoporous magnesium hydroxide nanoplateshave a multimodal size distribution.

The disclosure also relates to an antibacterial composition comprisingthe mesoporous magnesium hydroxide nanoplates that shows activityagainst E. coli, S. aureus, and/or K pneumoniae.

In some embodiments, the antibacterial composition further comprises asurfactant, a fragrance, a dye, a dispersant, a water softener, ableaching agent, and/or a foaming agent.

In some embodiments, the antibacterial composition further comprises abuffer or pH-control additive.

The disclosure also relates to a method of reducing a nitroaromaticcompound involvint mixing together the nitroaromatic compound, areducing agent, and the mesoporous magnesium hydroxide nanoplates.

In preferred embodiments, the reducing agent is sodium borohydride.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1A shows a powder XRD pattern of the Mg(OH)₂ nanoplates;

FIG. 1B shows a structural model of Mg(OH)₂ obtained after the analysisof the XRD pattern;

FIG. 2A is a TEM image of Mg(OH)₂ nanoplates at low magnification;

FIG. 2B is a TEM image of Mg(OH)₂ nanoplates at low magnification with aselected area highlighted;

FIG. 2C is a TEM image of Mg(OH)₂ nanoplates at low magnification;

FIG. 2D is a TEM image of Mg(OH)₂ nanoplates at moderate magnificationwith a selected area highlighted;

FIG. 2E is a TEM image of Mg(OH)₂ nanoplates at low magnification.

FIG. 2F is a TEM image of Mg(OH)₂ nanoplates at moderate magnification;

FIG. 2G is a TEM image of Mg(OH)₂ nanoplates at high magnification fromthe selected area of FIG. 2B;

FIG. 2H is a TEM image of Mg(OH)₂ nanoplates at high magnification fromthe selected area of FIG. 2D;

FIG. 2I shows a size distribution histogram of nanoplates calculatedfrom TEM images;

FIG. 3A shows a nitrogen adsorption-desorption BET isotherm of Mg(OH)₂nanoplates;

FIG. 3B. shows the corresponding BJH pore size distribution from the BETisotherm of FIG. 3A;

FIG. 4A shows data for the determination of MIC and MBC of Mg(OH)₂nanoplates against E. coli;

FIG. 4B shows data for the determination of MIC and MBC of Mg(OH)₂nanoplates against S. aureus;

FIG. 4C shows data for the determination of MIC and MBC of Mg(OH)₂nanoplates against IC pneumoniae;

FIG. 4D shows the radius of the zone of inhibition at differentconcentrations of Mg(OH)₂ nanoplates against selected bacteria by thewell diffusion method;

FIG. 5A shows the effect of control and sub-inhibitory concentration ofMg(OH)₂ nanoplates against biofilm formation for antibiotic-resistantbacteria;

FIG. 5B shows the effect of control and sub-inhibitory concentration ofMg(OH)₂ nanoplates against established biofilms for antibiotic-resistantbacteria;

FIG. 6A shows a plot of ln(A_(t)/A_(o)) versus time for the catalyticreduction of 4-NP in aqueous medium for two different concentrations ofMg(OH)₂ nanoplates as catalyst; and

FIG. 6B shows a plot of the percentage activity of the catalyst (Mg(OH)₂nanoplates) versus the number of cycles for the catalytic reduction of4-NP.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

Definitions

The phrase “substantially free”, unless otherwise specified, describes aparticular component being present in an amount of less than about 1 wt%, preferably less than about 0.5 wt. %, more preferably less than about0.1 wt. %, even more preferably less than about 0.05 wt %, yet even morepreferably 0 wt. %, relative to a total weight of the composition beingdiscussed.

As used herein, the terms “optional” or “optionally” means' that thesubsequently described event(s) can or cannot occur or the subsequentlydescribed component(s) may or may not be present (e.g., 0 wt. %).

As used herein, “inhibit” means prevent, hinder, reverse, remove,lessen, reduce an amount of, or delay the growth of a bacteria.

As used herein, “zone of inhibition” means an area of suitable bacterialgrowth medium around a sample of an antibiotic substance in whichbacteria do not grow due to action of the antibiotic substance.

As used herein, the term “solvothermal method” refers to a method ofproducing chemical compounds using a chemical reaction that takes placein a solvent other than pure water, preferably at a pressure above 1 barand at a temperature above the boiling point of the solvent atatmospheric pressure. A solvothermal method differs from a hydrothermalmethod in that the latter is restricted to using only water as thesolvent. Typically, if water is the only solvent used, the termhydrothermal method is preferred and solvothermal method refers solelyto methods that use solvents other than or in addition to water.

Method for Preparing Mesoporous Magnesium Hydroxide Nanoplates

According to a first aspect, the present disclosure relates to methodsof making mesoporous magnesium hydroxide nanoplates. Generally, themethod involves solvothermal techniques whereby a mixture of a magnesiumsource, a base, a glycol, and water are heated under solvothermalconditions. One advantage of the disclosed methods is that magnesiumhydroxide nanoplates can be formed with regular morphology without theneed forsurfactants and/or templates

A magnesium salt, a base, and a glycol having 2 to 6 carbons, preferably2 to 5 carbons, preferably 2 to 4 carbons, preferably 2 to 3 carbons,preferably 2 carbons may be mixed together in water to form an aqueousmixture. This aqueous mixture is preferably substantially free of asurfactant, a template, or both. The aqueous mixture may then besubjected to a solvothermal method at a temperature of 140 to 220° C.,preferably 150 to 210° C., preferably 160 to 200° C., preferably 170 to190° C., preferably 175 to 185° C. for a period of time from 2 to 24hours, preferably 3 to 20 hours, preferably 4 to 16 hours, preferably 5to 12 hours, preferably 6 to 10 hours, preferably 7 to 9 hours.

In preferred embodiments, the aqueous mixture is composed of a solventportion and a solute portion. In preferred embodiments, the solventportion is 55 to 99% (v/v), preferably 60 to 95% (v/v), preferably 70 to90% (v/v), preferably 75 to 85% (v/v), preferably 80% (v/v) water. Inpreferred embodiments, the remaining volume percent of the solventportion is the glycol having 2 to 6 carbons. While other organicsolvents may be used that are miscible with water, in preferredembodiments they are not. Such organic solvents may include, but are notlimited to, methanol, ethanol, acetone, acetaldehyde, acetic acid,acetonitrile, 2-butoxyethanol, butyric acid, diethanolamine,diethylenetriamine, dimethylformamide, dimethoxyethane, dimethylsulfoxide, 1,4-dioxane, ethylamine, formic acid, furfuryl alcohol,methyl diethanolamine, methyl isocyanide, N-methyl-2-pyrrolidone,1-propanol, 2-propanol, propanoic acid, pyridine, tetrahydrofuran, orthe like. In some embodiments, such organic solvents may be present inan amount of 0 to 40% (v/v), preferably 0 to 35% (v/v), preferably 0 to25% (v/v), preferably 0 to 15% (v/v), preferably 0 to 5% (v/v),preferably 0 to 1% (v/v) based on the total volume of the solventportion. In preferred embodiments, such organic solvents are not presentin the solvent portion. In preferred embodiments, the only organicsolvent present in the solvent portion is the glycol having 2 to 6carbons.

In preferred embodiments, the solute portion of the aqueous mixturecomprises a magnesium salt. In preferred embodiments, the magnesium saltis a water-soluble magnesium salt having a solubility greater than 1 gper 100 mL, preferably greater than 5 g per 100 mL, preferably greaterthan 10 per 100 mL, preferably greater than 25 g per 100 mL, preferablygreater than 50 g per 100 mL of water at 20° C. Such water-solublemagnesium salts may include, but are not limited to, magnesium acetate,magnesium bromate, magnesium bromide, magnesium chlorate, magnesiumchloride, magnesium chromate, magnesium fluorosilicate, magnesiumformate, magnesium iodate, magnesium iodide, magnesium molybdate,magnesium nitrate, magnesium perchlorate, magnesium selenite, magnesiumsulfate, and magnesium thiosulfate. The water-soluble magnesium salt maybe used in a hydrated or anhydrous state. In preferred embodiments, thewater-soluble magnesium salt is a magnesium halide, preferably magnesiumchloride, preferably magnesium chloride hydrate. In preferredembodiments, the magnesium salt is present in the aqueous mixture in anamount of 5 to 35 g/L, preferably 10 to 30 g/L, preferably 15 to 25 g/L,preferably 16 to 24 g/L, preferably 17 to 23 g/L, preferably 18 to 22g/L, preferably 18.5 to 21 g/L, preferably 19 to 20 g/L, preferably19.01 to 19.5 g/L, preferably 19.02 to 19.1 g/L, preferably 19.03 to19.06 g/L, preferably 19.05 g/L based on the total volume of the aqueousmixture.

In preferred embodiments, the solute portion of the aqueous mixturefurther comprises a base. In preferred embodiments, the base is amonoacidic base. Such a monoacidic base may include, but is not limitedto, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidiumhydroxide, cesium hydroxide, ammonium hydroxide, lithium bicarbonate,sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, cesiumbicarbonate, ammonium bicarbonate, lithium acetate, sodium acetate,potassium acetate, rubidium acetate, cesium acetate, ammonium acetate,or a hydroxide, bicarbonate, or acetate salt of an organoammonium cationhaving a general formula NH_(4-x)R_(x), where x=1, 2, 3, or 4, and R isan aryl, an alkyl, an alkylaryl, or an arylalkyl group. As used herein,“aryl” means a substituent derived from an aromatic ring, such asphenyl, benzyl, tolyl, xylyl, napthyl, halophenyl, pyramidyl, furyl,thiophenyl, pyrazinyl, quinolinyl, cinnamyl, styryl, and the like. Asused herein, “alkyl” means a saturated straight chain or branchednoncyclic hydrocarbon having from 1 to 30 carbon atoms. Representativesaturated straight chain alkyls include methyl, ethyl, n-propyl,n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl and thelike. Representative saturated branched alkyls include isopropyl,sec-butyl, isobutyl, tert-butyl, isopentyl, 2-methylbutyl,3-methylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2-methylpentyl,3-methylpentyl, 4-methylpentyl, 2-methylhexyl, 3-methylhexyl,4-methylhexyl, 5-methylhexyl, 2,3-dimethylbutyl, 2,3-dimethylpentyl,2,4-dimethylpentyl, 2,3-dimethyleyl, 2,4-dimethylhexyl, 2,5-dimethyleyl,2,2-dimethylpentyl, 2,2-dimethylhexyl, 3,3-dimethylpentyl,3,3-dimethylhexyl, 4,4-dimethylexyl, 2-ethylpentyl, 3-ethylpentyl,2-ethylhexyl, 3-ethylhexyl, 4-ethylhexyl, 2-methyl-2-ethylpentyl,2-methyl-3-ethylpentyl, 2-methyl-4-ethylpentyl, 2-methyl-2-ethylhexyl,2-methyl-3-ethylhexyl, 2-methyl-4-ethylhexyl, 2,2-diethylpentyl,3,3-dethylhexyl, 2,2-dethylhexyl, 3,3-dethylhexyl and the like. As usedherein, “arylalkyl” means an alkyl group as defined above substitutedwith an aryl group as defined about where the alkyl portion is connectedto the rest of the organoammonium cation. As used herein, “alkylaryl”means an aryl group as defined above substituted with an alkyl group asdefined above where the aryl portion is connected to the rest of theorganoammonium cation. In preferred embodiments, an acetate base isused, preferably sodium acetate. In preferred embodiments, the base ispresent in the aqueous mixture in an amount of 5 to 60 g/L, preferably10 to 55 g/L, preferably 15 to 50 g/L, preferably 20 to 45 g/L,preferably 25 to 40 g/L, preferably 30 to 35 g/L, preferably 31 to 34g/L, preferably 32 to 33 g/L, preferably 32.5 to 33.9 g/L, preferably32.75 to 32.85 g/L, preferably 32.80 to 32.83 g/L, preferably 32.81 to32.82 g/L based on the total volume of the aqueous mixture.

In preferred embodiments, the ratio of the moles of base present in theaqueous mixture to the moles of magnesium present in the aqueous mixtureis 1:1 to 3:1, preferably 1.5:1 to 2.5:1, preferably 1.75:1 to 2.25:1,preferably 2:1.

In preferred embodiments, the glycol having 2 to 6 carbons may beethylene glycol, propylene glycol, 1,2-butanediol, 2,3-butanediol,1,2-pentanediol, 2,3-pentanediol, 1,2-hexanediol, 2,3-hexanediol, or3,4-hexanediol. In preferred embodiments, ethylene glycol is 12 used. Inpreferred embodiments, the glycol is present in the aqueous mixture inan amount of to 45% (v/v), preferably 10 to 35% (v/v), preferably 15 to25% (v/v), preferably 16 to 24% (v/v), preferably 17 to 23% (v/v),preferably 18 to 22% (v/v), preferably 20% (v/v) based on the totalvolume of the aqueous mixture. In preferred embodiments, ethylene glycolis the only glycol used. While mixtures of glycols satisfying the abovecriteria may be used, preferably a single glycol is used.

The aqueous mixture described above is preferably substantially free ofa surfactant, template, or both. As defined here, a surfactant is acompound that lowers the surface tension (or interfacial tension)between two liquids, between a liquid and a gas, or between a liquid anda solid. The surfactant may be a nonionic surfactant, an anionicsurfactant, a cationic surfactant, a viscoelastic surfactant, or azwitterionic surfactant. The surfactant may also be a gemini surfactantof any of the types listed previously. The surfactant may serve a roleas a water-wetting agent, a defoamer, a foamer, a detergent, adispersant, or an emulsifier.

A surfactant molecule comprises one or more hydrophilic head unitsattached to one or more hydrophobic tails. The tail of most surfactantscomprises a hydrocarbon chain, which can be branched, linear, oraromatic. Fluorosurfactants have fluorocarbon chains. Siloxanesurfactants have siloxane chains. Gemini surfactant molecules comprisetwo or more hydrophilic heads and two or more hydrophobic tails.

Many surfactants include a polyether chain terminating in a highly polaranionic group. The polyether groups often comprise ethoxylated(polyethylene oxide-like) sequences inserted to increase the hydrophiliccharacter of a surfactant. Alternatively, polypropylene oxides may beinserted to increase the lipophilic character of a surfactant.

Anionic surfactants contain anionic functional groups at their head,such as sulfate, sulfonate, phosphate, and carboxylate. The anionicsurfactant may be an alkyl sulfate, an alkyl ether sulfate, an alkylester sulfonate, an alpha olefin sulfonate, a linear alkyl benzenesulfonate, a branched alkyl benzene sulfonate, a linear dodecylbenzenesulfonate, a branched dodecylbenzene sulfonate, an alkyl benzenesulfonic acid, a dodecylbenzene sulfonic acid, a sulfosuccinate, asulfated alcohol, a ethoxylated sulfated alcohol, an alcohol sulfonate,an ethoxylated and propoxylated alcohol sulfonate, an alcohol ethersulfate, an ethoxylated alcohol ether sulfate, a propoxylated alcoholsulfonate, a sulfated nonyl phenol, an ethoxylated and propoxylatedsulfated nonyl phenol, a sulfated octyl phenol, an ethoxylated andpropoxylated sulfated octyl phenol, a sulfated dodecyl phenol, and anethoxylated and propoxylated sulfated dodecyl phenol. Other anionicsurfactants include ammonium lauryl sulfate, sodium lauryl sulfate(sodium dodecyl sulfate, SLS, or SDS), and related alkyl-ether sulfatessodium laureth sulfate (sodium lauryl ether sulfate or SLES), sodiummyreth sulfate, docusate (dioctyl sodium sulfosuccinate),perfluorooctanesulfonate (PFOS), perfluorobutanesulfonate, alkyl-arylether phosphates, and alkyl ether phosphates.

Cationic surfactants have cationic functional groups at their head, suchas primary and secondary amines. Cationic surfactants include octenidinedihydrochloride; cetrimonium bromide (CTAB), cetylpyridinium chloride(CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT),dimethyldioctadecylammonium chloride, and dioctadecyldimethylammoniumbromide (DODAB).

Zwitterionic (amphoteric) surfactants have both cationic and anionicgroups attached to the same molecule. Zwitterionic surfactants includeCHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate),cocamidopropyl hydroxysultaine, ocamidopropyl betaine, phospholipids,and sphingomyelins.

Nonionic surfactants have a polar group that does not have a charge.These include long chain alcohols that exhibit surfactant properties,such as cetyl alcohol, stearyl alcohol, 14 cetostearyl alcohol, oleylalcohol, and other fatty alcohols. Other long chain alcohols withsurfactant properties include polyethylene glycols of various molecularweights [Pilarska, et. al. 2012, Physicochem. Probl. Miner. Process. 48,2, 631-643], polyethylene glycol alkyl ethers having the formulaCH3-(CH2)10-16-(O—C2H4)1-25-0H, such as octaethylene glycol monododecylether and pentaethylene glycol monododecyl ether; polypropylene glycolalkyl ethers having the formula: CH3- (CH2)10-16-(O—C3H6)1 25-0H;glucoside alkyl ethers having the formula CH3-(CH2)10-160-glucoside)1-3-0H, such as decyl glucoside, lauryl glucoside, octylglucoside; polyethylene glycol octylphenyl ethers having the formulaC8H17-(C6H4)—(O—C2H4)1-25-0H, such as Triton X-100; polyethylene glycolalkylphenyl ethers having the formula C9H19 (C6H4)—(O—C2H4)1-25-0H, suchas nonoxynol-9; glycerol alkyl esters such as glyceryl laurate;polyoxyethylene glycol sorbitan alkyl esters such as polysorbate,sorbitan alkyl esters, cocamide MEA, cocamide DEA, dodecyldimethylamineoxide, block copolymers of polyethylene glycol and polypropylene glycol,such as poloxamers, and polyethoxylated tallow amine (POEA).

A dendritic surfactant molecule may include at least two lipophilicchains that have been joined at a hydrophilic center and have abranch-like appearance. In each dendritic surfactant, there may be fromabout 2 lipophilic moieties independently to about 4 lipophilic moietiesattached to each hydrophilic group, or up to about 8 lipophilic moietiesattached to the hydrophilic group for example. “Independently” as usedherein with respect to ranges means that any lower threshold may becombined with any upper threshold. The dendritic surfactant may havebetter repulsion effect as a stabilizer at an interface and/or betterinteraction with a polar oil, as compared with other surfactants.Dendritic surfactant molecules are sometimes called “hyperbranched”molecules.

A dendritic extended surfactant is a dendritic surfactant having anon-ionic spacer arm between the hydrophilic group and a lipophilictail. For example, the non-ionic spacer-arm extension may be the resultof polypropoxylation, polyethoxylation, or a combination of the two withthe polypropylene oxide next to the tail and polyethylene oxide next tothe head. The spacer arm of a dendritic extended surfactant may containfrom about 1 independently to about 20 propoxy moieties and/or fromabout 0 independently to about 20 ethoxy moieties. Alternatively, thespacer arm may contain from about 2 independently up to about 16 propoxymoieties and/or from about 2 independently up to about 8 ethoxymoieties. “Independently” as used herein with respect to ranges meansthat any lower threshold may be combined with any upper threshold. Thespacer arm extensions may also be formed from other moieties including,but not necessarily limited to, glyceryl, butoxy, glucoside, isosorbide,xylitols, and the like. For example, the spacer arm of a dendriticextended surfactant may contain both propoxy and ethoxy moieties: Thepolypropoxy portion of the spacer arm may be considered lipophilic;however, the spacer arm may also contain a hydrophilic portion to attachthe hydrophilic group. The hydrophilic group may generally be apolyethoxy portion having about two or more ethoxy groups. Theseportions are generally in blocks, rather than being randomly mixed.Further, the spacer arm extension may be a poly-propylene oxide chain.

Another type of surfactant is a viscoelastic surfactant (VES).Conventional surfactant molecules are characterized by having one longhydrocarbon chain per surfactant head-group. In a viscoelastic gelledstate these molecules aggregate into worm-like micelles. A viscoelasticgel is a gel that has elastic properties, meaning that the gel at leastpartially returns to its original form when an applied stress isremoved. Typical viscoelastic surfactants includeN-erucyl-N,N-bis(2-hydroxyethyl)-N-methyl ammonium chloride andpotassium oleate, solutions of which form gels when mixed with inorganicsalts such as potassium chloride and/or with organic salts such assodium salicylate. Previously described surfactants may also beconsidered viscoelastic surfactants.

As used herein, a template refers to a material added to the aqueousmixture during the preparation of magnesium hydroxide particles that maydirect or influence the crystallization of magnesium hydroxide to affectthe size, shape, porosity, or other physical characteristic of themagnesium hydroxide particle and is not a surfactant. Examples of suchtemplates include, but are not limited to, gelatin [Femitha, et. al.,2016, Green Chemistry and Technology Letters, 2, 2, 87-90], cellulosegel [Han, et. al., 2015, ACS Sustainable Chem. Eng. 3, 8, 1853-1859],agar [Ambrose, et. al., 1983, Proc. Indian Acad. Sci, 92, 3, 237-247],spider silk [Dimitrovic, et. al., 2018, Chemical Industry, 72, 1,23-28], walnut shell [Zamani, et. al. 2019, Green Processing andSynthesis, 8, 1, 199-206], or a magnesium carbonate hydroxide [Chen, et.al., 2018, Journal of Central South University, 25, 4, 729-735].

In some embodiments, the components of the aqueous mixture are added atthe same time. In preferred embodiments, the aqueous mixture is formedby mixing the magnesium salt and the base in water before adding theglycol. In some embodiments, there is a first mixing period that thecombination of water, magnesium salt, and base is subjected to beforeadding the glycol. In preferred embodiments, this first mixing period is1 to 30 minutes, preferably 5 to 25 minutes, preferably 10 to 20minutes, preferably 15 minutes. Following this first mixing period theglycol may be added. In some embodiments, after adding the glycol, thereis a second mixing period before heating. In preferred embodiments, thesecond mixing period is 1 to 30 minutes, preferably 5 to 25 minutes,preferably 10 to 20 minutes, preferably 15 minutes.

In some embodiments, following the second mixing period the aqueousmixture is heated to 140 to 220° C. and maintained at that temperaturefor a period of time to allow for the formation of the nanoplates. Inpreferred embodiments, the aqueous mixture is heated to 140 to 220° C.,preferably 150 to 210° C., preferably 160 to 200° C., preferably 170 to190° C., preferably 175 to 185° C., preferably 180° C. In preferredembodiments, the heating step is performed under solvothermalconditions. In preferred embodiments, the heating is maintained for aperiod of time from 2 to 24 hours, preferably 3 to 20 hours, preferably4 to 16 hours, preferably 5 to 12 hours, preferably 6 to 10 hours,preferably 7 to 9 hours. In preferred embodiments, the solvothermalreaction is performed in a vessel capable of withstanding an internalpressure of 1200 to 3500 psig, preferably 1500 to 3450 psig, preferably1750 to 3400 psig, preferably 1800 to 3350 psig, preferably 1900 to 3300psig. In preferred embodiments, the vessel is lined withpolytetrafluoroethylene (PTFE).The use of a vessel capable ofwithstanding elevated internal pressures is required to meet thecriteria outlined above for the method to qualify as a “solvothermal”method.

Following the heating step, the nanoplates may be collected by anysolid-liquid separation technique known to those of ordinary skill inthe art, for example, filtration, decantation, centrifugation, or thelike, but excluding techniques such as evaporation. In preferredembodiments, the nanoplates are collected by centrifugation at 500 to5000 rpm, preferably 750 to 4500 rpm, preferably 1000 to 4000 rpm toform a pellet. In some embodiments, this pellet may be washed with asolvent to remove any impurities from the mesoporous magnesium hydroxidenanoplates. In preferred embodiments the solvent is one in whichmagnesium hydroxide has a solubility below 0.1 g per 100 mL, preferablybelow 0.05 g per 100 mL, preferably below 0.01 g per 100 mL, preferablybelow 0.005 g per 100 mL, preferably below 0.001 g per 100 mL,preferably below 0.00064 g per 100 mL of solvent at 25° C. Examples ofsuch solvents include but are not limited to distilled water, methanol,ethanol, and acetone. In some embodiments, the pellet is washed morethan one time. In preferred embodiments, the pellet is washed with morethan one solvent. In preferred embodiments, the pellet is washed morethan one time with a first solvent, then more than one time with asecond solvent. In some embodiments, the pellet may be washed additionaltimes with additional solvents. In preferred embodiments, the firstsolvent is water and the pellet is washed with water three times. Inpreferred embodiments, the second solvent is methanol and the pellet iswashed with methanol three times. Following the washings, the pellet maybe dried, for example, by allowing the pellet to dry in ambientatmosphere, an inert atmosphere, or by subjecting the pellet tor vacuum.In preferred embodiments, the pellet is dried under vacuum. In someembodiments, the pellet is dried at room temperature. In preferredembodiments, the pellet is dried at 30 to 90° C., preferably 40 to 80°C., preferably 50 to 70° C., preferably at 60° C.

In preferred embodiments, the mesoporous magnesium hydroxide nanoplatesproduced using the method have a diameter of 1Q to 200 nm, preferably 11to 190 rim, preferably 12 to 180 nm, preferably 13 to 170 nm, preferably14 to 160 nm, preferably 15 to 150 nm, preferably 16 to 140 nm,preferably 17 to 130 nm, preferably 18 to 120 nm, preferably 19 to 110nm, preferably 20 to 100 nm. In some embodiments, the mesoporousmagnesium hydroxide nanoplates have a multimodal distribution ofdiameters where the mean still falls within the aforementioned range. Inpreferred embodiments, the multimodal distribution of diameters isbimodal. Preferably, a first mode of the distribution of diameters is 10to 60 nm, preferably 15 to 55 nm, preferably 20 to 50 nm, preferably 25to 45 nm. Preferably, a second mode of the distribution of diameters is60 to 100 run, preferably 65 to 95 rim, preferably 70 to 90 nm. Inpreferred embodiments, the second mode is predominant. In preferredembodiments, the mesoporous magnesium hydroxide nanoplates aremonodisperse with a coefficient of variation, defined as the ratio ofthe standard deviation to the mean diameter, of less than 10%,preferably less than 9%, preferably less than 8%, preferably less than7%, preferably less than 6%, preferably less than 5%, preferably lessthan 4%, preferably less than 3%, preferably less than 2%. Inembodiments with a multimodal distribution of diameters, the nanoplatesmay be monodisperse as per the above definition centered around each ofthe modes. In preferred embodiments, the mesoporous magnesium hydroxidenanoplates have a uniform shape similar to that of a circular disc. Theflat portion of the nanoplates may be described using a circularitydefined as 4π(Area)/(Perimeter)² which may vary from 0 for a1-dimensional object to 1 for a perfect circle. In preferredembodiments, the mesoporous magnesium hydroxide nanoplates have acircularity of at least 0.6, preferably at least 0.7, preferably atleast 0.8, preferably at least 0.9.

In preferred embodiments, the mesoporous magnesium hydroxide nanoplateshave a uniform shape with a circularity coefficient of variation,defined as the ratio of the standard deviation to the mean circularity,of less than 10%, preferably less than 9%, preferably less than 8%,preferably less than 7%, preferably less than 6%, preferably less than5%, preferably less than 4%, preferably less than 3%, preferably lessthan 2%. In preferred embodiments, the plates have a thickness of 0.5 to30 nm, preferably 1 to 25 nm, preferably 2 to 20 nm, preferably 5 to 15nm. In preferred embodiments, the plates are hollow, having athin-walled shell surrounding an interior void. In preferredembodiments, the thin-walled shell has a thickness of 0.1 to 10 nm,preferably 0.5 to 7.5 nm, preferably 1 to 5 nm.

In preferred embodiments, the mesoporous magnesium hydroxide nanoplateshave a mean pore diameter of 2 to 50 nm, preferably 2.5 to 40 nm,preferably 3 to 30 nm, preferably 3.5 to 20 nm, preferably 4 to 10 nm,preferably 5 to 9 nm. In preferred embodiments, these pores are ofuniform size, having a coefficient of variation less than 10%,preferably less than 9%, preferably less than 8%, preferably less than7%, preferably less than 6%, preferably less than 5%, preferably lessthan 4%, preferably less than 3%, preferably less than 2%. In preferredembodiments, the pores are ordered, meaning that they have a regulararrangement that repeats throughout the volume of the nanoplate. Inpreferred embodiments, the mesoporous magnesium hydroxide nanoplateshave a surface area of 10 to 110 m²/g, preferably 20 to 100 m²/g,preferably 30 to 90 m²/g, preferably 40 to 80 m²/g, preferably 50 to 70m²/g, preferably 55 to 65 m²/g, preferably 57.5 to 62.5 m²/g, preferably59 to 60 m²/g.

In preferred embodiments, the mesoporous magnesium hydroxide nanoplateshave a type-III nitrogen adsorption-desorption BET isotherm. Inpreferred embodiments, the isotherm also displays a H3 hysteresis loop.

Antibacterial Composition

The mesoporous magnesium hydroxide nanoplates produced by the methoddescribed above may find use in an antibacterial composition. Themesporous nature and high surface area of the nanoplates produced by themethod may be advantageous for antibacterial effects. The nanoplatesshow antibacterial activity against both gram positive and gram negativebacteria as described below. These nanoplates may be used as a componentin an antibacterial composition that takes the form of a solid, liquid,gel, foam, dispersion, colloid, or other type of mixture. In someembodiments, the nanoplates are homogenously distributed throughout thevolume of the mixture. In some embodiments, the nanoplates arenon-homogenously distributed throughout the volume of the mixture. Insome embodiments, the nanoplates may separate from other components ofthe mixture and require mixing or redispersion before use.

Magnesium hydroxide is generally recognized as safe by the US FDA and isapproved for use as a food additive in the European Union (E528). Theantibacterial composition comprising the nanoplates may find use as afood additive. In some embodiments, the nanoplates may be added directlyto a foodstuff to form an antibacterial composition that comprises thenanoplates and the components of the foodstuff. In some embodiments, theantibacterial composition is pre-formed from other components beforebeing added to the foodstuff.

Magnesium hydroxide is currently a common component in many cosmeticsand bath products. The antibacterial composition may also find use insuch products. In some embodiments, the antibacterial compositioncomprising the nanoplates is such a cosmetic or bath product. In someembodiments, the antibacterial composition is a component of a cosmeticor bath product that shows antibacterial activity. Examples of suchcosmetics Qr bath products include but are not limited to soaps, facialsoaps, facial washes, body washes, shampoos, conditioners, deodorants,antiperspirants, combination deodorants/antiperspirants, fragrances,foot powders, hair dyes or colors, makeup, nail products, personalcleanliness products, shaving products, depilatories, skincare products,tanning products, body or face creams, moisturizers, and anti-acneproducts.

In some embodiments, the antibacterial composition is not intended forbodily contact or ingestion. In some embodiments, the antibacterialcomposition is intended to be used in a container, pipe, reservoir, orother such vessel intended to store or transport material, or on asurface. In some embodiments the antibacterial composition is designedto be transiently contacted with the vessel or surface and then removed.In some embodiments, the antibacterial composition is designed to be incontact with the vessel or surface for an extended period of timeincluding the lifetime of either the antibacterial composition or thevessel or surface.

In some embodiments, the antibacterial composition further comprises asurfactant. A surfactant may be present at a weight percentage in arange of 0.02-10 wt %, preferably 0.1-5 wt %, more preferably 0.5-2 wt%. Examples of surfactants and surfactants types that may be included inthe antibacterial composition may be those surfactants/surfactant typesdescribed previously.

In one embodiment, the antibacterial composition may further comprise amutual solvent. A mutual solvent may be present at a weight percentageof 1-20 wt %, preferably 3-15 wt %, more preferably 4-12 wt %. Asdefined herein, a “mutual solvent” is a liquid that is substantiallysoluble in both aqueous and oleaginous fluids, and may also be solublein other well treatment fluids. As defined here, “substantially soluble”means soluble by more than 10 grains mutual solvent per liter fluid,preferably more than 100 grams per liter. Mutual solvents are routinelyused in a range of applications, controlling the wettability of contactsurfaces before and preventing or stabilizing emulsions.

Examples of the mutual solvent include propylene glycol, ethyleneglycol, diethylene glycol, glycerol, and 2-butoxyethanol. In a preferredembodiment, the mutual solvent is 2-butoxyethanol, which is also knownas ethylene glycol butyl ether (EGBE) or ethylene glycol monobutyl ether(EGMBE). In alternative embodiments, the mutual solvent may be one oflower alcohols such as methanol, ethanol, 1-propanol, 2-propanol,n-butanol, n-hexanol, 2-ethylhexanol, and the like, other glycols suchas dipropylene glycol, polyethylene glycol, polypropylene glycol,polyethylene glycol-polyethylene glycol block copolymers, and the like,and glycol ethers such as 2-methoxyethanol, diethylene glycol monomethylether, and the like, substantially water/oil-soluble esters, such as oneor more C2-esters through C10-esters, and substantiallywater/oil-soluble ketones, such as one or more C2-C10 ketones.

In some embodiments, the antibacterial composition may further comprisea buffer. As used herein, a buffer (more precisely, pH buffer orhydrogen ion buffer) refers—to a mixture of a weak acid and itsconjugate base, or vice versa. Its pH changes very little when a smallor moderate amount of strong acid or base is added to it and thus it isused to prevent changes in the pH of a solution. Buffer solutions areused as a means of keeping pH at a nearly constant value in a widevariety of chemical applications. Examples of buffers include, but arenot limited to, HEPES buffer, TAPS, Bicine, Glycylglycine, Tris, HEPPSO,EPPS, HEPPS, POPSO, N-ethylmorpholine, TEA (Triethanolamine), Tricine,TAPSO, DIPSO, TES, BES, phosphoric acid, MOPS, imidazole PIPES and thelike.

In one embodiment, the antibacterial composition may further compriseother components, such as alcohols, glycols, organic solvents,fragrances, dyes, dispersants, non-buffer pH control additives, acids orbases, water softeners, bleaching agents, foaming agents, antifoamingagents, catalysts, corrosion inhibitors, corrosion inhibitorintensifiers, viscosifiers, diverting agents, oxygen scavengers, carrierfluids, fluid loss control additives, friction reducers, stabilizers,theology modifiers, gelling agents, scale inhibitors, breakers, salts,crosslinkers, salt substitutes, relative permeability modifiers, sulfidescavengers, fibers, microparticles, bridging agents, shale stabilizingagents (such as ammonium chloride, tetramethyl ammonium chloride, orcationic polymers), clay treating additives, polyelectrolytes,non-emulsifiers, freezing point depressants, iron-reducing agents, otherbiocides/bactericides and the like, provided that they do not interferewith the antibacterial activity of the nanoplates as described herein.

Method of Reducing Nitroaromatic Compounds

The mesoporous magnesium hydroxide nanoplates produced by the methodabove may find use in a method for reducing nitroaromatic compounds Sucha method involves mixing together a nitroaromatic compound, a reducingagent, and the mesoporous magnesium hydroxide nanoplates. The mesoporousnature and high surface area of the nanoplates produced by the abovemethod may be advantageous in accelerating the rate of the reduction ofthe nitroaromatic compounds. In preferred embodiments, this mixing steptakes place in a solvent which can dissolve the nitroaromatic compound.In preferred embodiments, the nanoplates are present in an amount of 1to 1000 ppm, preferably 10 to 500 ppm, preferably 50 to 150 ppm based onthe total amount of the reaction mixture. In preferred embodiments, therate of the reaction is accelerated by a factor of 1 to 10,000%,preferably 2 to 5,000%, preferably 5 to 1,000% of the rate of theuncatalyzed reaction.

As used herein, a nitroaromatic compound refers to a compound which hasone or more aromatic rings and one or more nitro functional groups(—NO₂) attached to the aromatic ring(s). Examples of nitroaromaticcompounds include, but are not limited to, 4-nitrophenol, nitrobenzene,p-nitrotoluene, p-nitrochlorobenzene, 2,6-dinitrotoluene,o-dinitrobenzene, p-dinitrobenzene, 1-nitronaphthalene,2-nitronaphthalene, 4-nitrobiphenyl, and 2,4,6-trinitrotoluene. Inpreferred embodiments, the product of the reduction reaction is ananiline.

In some embodiments, the nitroaromatic compound, reducing agent, andmesoporous magnesium hydroxide nanoplates are mixed in a solvent.Solvents that may be used include an aprotic organic solvent, a proticorganic solvent, or preferably, water. Examples of aprotic organicsolvents include but are not limited to diethyl ether, tetrahydrofuran,acetonitrile, acetone, N,N-dimethylformamide, dimethylsulfoxide,pentane, hexanes, cyclohexane, benzene, toluene, chloroform,dichloromethane, and ethyl acetate. Examples of protic organic solventsinclude but are not limited to ammonia, t-butanol, n-butanol,n-propanol, 2-propanol, ethanol, and methanol. In some embodiments, theaprotic organic solvent or protic organic solvent is substantially freeof water, oxygen, or both. In preferred embodiments, the solvent isdeionized water.

The method for reducing nitroaromatic compounds involves the use of areducing agent. In some embodiments, the reducing agent is soluble inthe solvent. Examples of soluble reducing agents include but are notlimited to sodium hydrosulfite, sodium sulfide, tin (II) chloride,titanium (III) chloride, hydroiodic acid, hydrazine, lithium aluminumhydride, borohydrides and borohydride salts such as sodium borohydride,and alkali metal hydrides. In some embodiments, the reducing agent isinsoluble in the solvent. Examples of insoluble reducing agents includezinc, samarium, Raney nickel, platinum-on-carbon, and iron. In preferredembodiments, sodium borohydride is used. In preferred embodiments, themole ratio of the amount of sodium borohydride to the amount of thenitroaromatic compound is 0.5 to 100, preferably 0.75 to 50, preferably0.80 to 10, preferably 0.9 to 1.5. In some embodiments, the nanoplatesare present in an amount of 1 to 1000 mg/L., preferably 5 to 500 mg/L,preferably 10 to 250 mg/L, preferably 25 to 100 mg/L, preferably 50 to75 mg/L based on the total volume of the reaction mixture.

The examples below are intended to further illustrate protocols forpreparing and characterizing the nanoplates, preparing andcharacterizing the antibacterial composition, and performing thereduction of nitroaromatic compounds and are not intended to limit thescope of the claims.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

As used herein the words “a” and “an” and the like carry the meaning of“one or more.”

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

EXAMPLES Results and Discussion

Characterization of Magnesium Hydroxide Nanoplatelets

X-Ray Powder Diffraction

The composition and structural parameters of the prepared product wereinvestigated by XRD. The XRD pattern is shown in FIG. 1A. Diffractionpeaks were observed at 20 values 18.50°, 32.78°, 38.07°, 50.74°, and58.65°, which clearly indicate that the product is magnesium hydroxide(Mg(OH)₂) (PDF #96-210-1439). The Miller indices (hi(1) and d-spacing ofthese peaks are given in Table 1. Mg(OH)₂ belong to the space group P-3ml with space group number 164. It belongs to the trigonal crystalsystem. The values of unit cell parameters and atomic coordinates werecalculated and are given in Table 1. These values are used to constructthe structural model of Mg(OH)₂ given in FIG. 1B. Magnesium is presentat the corners while oxygen and hydrogen are present within the unitcell. All the eight corners are occupied by magnesium (green spheres).Two oxygen atoms (red spheres) and two hydrogen atoms (blue spheres) arepresent per unit cell. Position of one hydrogen atom is represented bythree blue spheres in FIG. 1B according to the three-site split-atommodel. Because of the unusual thermal motion of the hydrogen atom, asingle hydrogen atom is distributed into three positions with equaloccupation rate [L. Desgranges, G. Calvarin, G. Chevrier, ActaCrystallogr. B 1996, 52, 82]. The Mg—Mg bond distances along y— andz-axis were calculated and are given in Table 1. The O—H and H—H bonddistances are also given in Table 1.

TABLE 1 Details of various structural parameters of Mg(OH)₂ obtainedfrom XRD pattern Property Details Name Magnesium hydroxide Chemicalformula Mg(OH)₂ Space group P-3 ml (164) Crystal system Trigonal(hexagonal axes) No. of formula units per unit cell 1 Unit cellparameters Lengths (Å) a = 3.1480 c = 4.7790 Angles (°) α = 90.0 and γ =120.0 Atomic coordinates Mg x = 0.000, y = 0.000, and z = 0.000 O x =0.333, y = 0.667, and z = −0.219 H x = 0.362, y = 0.638, and z = −0.416Distances (Å) Mg—Mg (along z-axis) 3.148 Mg—Mg (along y-axis) 4.77900O—O 3.24296 O—H 0.95435 H—H 1.70567 2θ (°), d-spacing (Å) and 18.50,4.7790, and (0 0 1) Miller indices 32.78, 2.7262, and (1 0 0) (hkl)38.07, 2.3680, and (0 1 1) 50.74, 1.7970, and (0 1 2) 56.65, 1.5740, and(1 1 0)

Transmission Electron Microscopy

In order to investigate the morphology of the Mg(OH)₂ product, TEM wasused, and the results are shown in FIG. 2A-2H. FIG. 2A-2D show theoverview of the product. It is clear from these figures that the productis well separated and no agglomeration is present among the particles ofMg(OH)₂.

There are two types of particles present in the product. One is smallerwith a narrow size range 20-50 nm, and the other is relatively largewith the size range 50-100 nm. Overall, the size distribution of productranges from 20 to 100 nm. The size of many nanoplatelets was calculatedfrom the TEM images along their longest diameter, and the sizedistribution histogram was constructed (FIG. 21 ). This plot shows twomaxima, which show that two size ranges are present. One type ofparticles is small while the other type is large. Descriptive statisticswere performed on the size distribution data using OriginPro 8. Themean, median, mode, kurtosis, and skewness were calculated for bothtypes of particles, which were found to be 35.85, 34.84, 34.84, −1.02,−0.037, respectively, for small particles. The values of mean, median,and mode are very close to each other. The value of skewness is −0.03and the value of kurtosis is less than 3. This confirms that the datasetis normally distributed (Gaussian distribution). The values of mean,median, mode, kurtosis, and skewness were found to be 79.07, 80, 85.97,−1.04, −0.4, respectively, for the large particles. The values of meanand median lie close to each other but the value of mode does not lieclose to the mean and median values. The values of kurtosis and skewnessare also greater than 0.03 and 3, respectively. These deviations in thevalues indicate that size distribution of the large particles is notnormal. This size distribution shows that the product is formed by theOstwald ripening mechanism, which affects their Gaussian sizedistribution. These particles have platelet-like morphology withirregular edges. These nanopartides are very thin-layered, and thehigh-resolution image of these nanoparticles shows a contrast of darkand light colors, which might be attributed to the thin walls (only afew atoms thick walled platelets) with porous morphology or to theirhollow inside. A closer look of these nanoparticles reveals that thesurface of these particles is not smooth but rough. The rough surfacesupports the presence of pores, so it can be assumed that the productconsists of porous nanoplatelets of Mg(OH)₂.

Surface Analysis

FIG. 3 displays the nitrogen adsorption-desorption isotherm and thecorresponding Barrett Joyner-Halenda (BJH) pore size distribution curve(the insert) of the samples. It can be seen that the isotherm ischaracterized by the distinct type-III curve with H3 hysteresis loop,which is characteristic of mesoporous structural materials with ahysteresis loop. Moreover, it is seen that the BJH pore sizedistribution is narrow with uniform pores with a well-organized, orderedporosity with a pore size of 5.01 nm. The Bnnauer-Emmett Teller (BET)specific surface area was 59.2 m²/g. Compared to that of the bulksamples, the pore size exhibits a narrower distribution as the reactiontemperature is increased; it has also a relatively highsurface-to-volume ratio.

Formation Mechanism

Statistical data analysis showed that the nanoplatelets possess arhombic structure. During the growth process, rhombic unit cells arearranged to form the nanoplatelet morphology. Mg(OH)₂ nanoplatelets areformed by the following reaction mechanism:

Antibacterial Application

Determination of the MIC and MBC MIC and MBC of all tested bacterialstrains against Mg(OH)₂ nanoplatelets were tested with the help of theredox dye nitro-blue tetrazolium chloride (NBT). NBT λ_(max) 630 nm)absorbs in the visible region, so it was used to count the number ofviable bacterial cells (Beer-Lambert law). NBT is positively charged,while the bacterial wall is negatively charged because of the presenceof lipids and other moieties. So NBT gets easily adsorbed on the surfaceof bacteria and makes visible the presence of bacteria. A plot of theabsorbance as a function of the concentration of Mg(OH)₂ nanoplateletsis shown in FIG. 4A. It is observed that number of bacteria decreasedwith the increase in concentration of the Mg(OH)₂ nanoplatelets. The MICof the nanoplatelets against E. coli, K. pneumonia, and S. aureusstrains was 250, 500, and 500 μg/mL respectively. The MBC of thenanoplatelets against all tested strains was 1,000 μg/mL. Thenanoplatelets showed maximum activity against E. coli and minimumactivity against S. aureus. This might be due to the difference in thecell wall composition of the strains. Although E. coli and K. pneumoniaeare both Gram-negative strains, the MIC values of the nanoplateletsagainst these Gram-negative strains are different. This shows that somefactors other than the cell wall composition are also involved in theantibacterial activity of Mg(OH)₂ nanoplatelets.

Investigation of dose-dependent antibacterial activity Thedose-dependent bactericidal activity of the nanoplatelets was studied bythe well diffusion method. The diameter of the zone of inhibition wasmeasured to evaluate the growth of bacteria. The bactericidal activitywas studied in the range of concentration 1,000 3,000 μg/mL of thenanoplatelets against all bacterial strains. This concentration range ishigher than the MIC and MBC of the nanoplatelets against all strains. Itcan be observed from FIG. 4B that the diameter of the zone of inhibitionincreased with the increase in concentration of the nanoplatelets. Theavailable surface area increases with the increase in concentration ofthe nanoplatelets, so the antibacterial activity increases with increasein dose. The maximum activity was observed against S. aureus followed byE. coli and K pneumoniae. The cell wall thickness of Gram negativebacteria is smaller than that of Gram-positive bacteria, so theantibacterial action of the nanoplatelets is more pronounced in case ofthe former (S. aureus) compared to that of the latter (E. coli and K.pneumoniae). Mg(OH)₂ nanoplatelets adhere to the surface of bacteriainitially and then diffuse into the cells through the porous membrane.Mg(OH)₂ nanoplatelets are of very small size, so they can easily producealterations in the chemical reaction series within the cells. Thiscauses the disruption of the cells and kills bacteria.

Evaluation of Mg(OH)₂ Nanoplatelet Activity on Biofilm Formation

The effect of sub-inhibitory concentration (0.5×MIC) of Mg(OH)₂nanoplatelets on biofilm formation of the three selected strains wasmeasured by using microtiter plate assay. Biofilm formation wasquantified after 48, 72, 96, and 120 hr after staining the adhered cellswith crystal violet (CV) (FIG. 5A). For all three tested strains,maximum biofilm forming capacity was observed after 96 hr of incubationin control and treated cells. Biofilm formation decreased when theduration of interaction was increased from 96 to 120 hr. The results ofabsorbance at 546 nm revealed that K pneumoniae had the highest abilityto form biofilms, followed by S. aureus and E. coli. Moreover, thebiofilm formation decreased with increase in the duration of contact ofthe nanoplatelets. The ability of Mg(OH)₂ nanoplatelets to exhibitantibiofilm properties against already established mature biofilms wasalso studied using microliter plate assay at intervals of 48, 72, 96,and 120 hr. After a given time interval, the biofilms formed by thebacterial strains were exposed to nanoplatelets (0.5×MIC) for 24 hr. Theresults revealed that K pneumoniae had a greater capacity to formbiofilm in comparison with E. coli and S. aureus (FIG. 5B). Fortyeight-hour-old biofilms treated with the nanoplatelets showed moredecline in biofilm viability than 72-hr-old biofilms. Thus with thepassage of time, the nanoplatelets showed less ability to decreasebiofilm viability. All the three selected strains (E. coli, K.pneumonia, and S. aureus) displayed the same trend. Similarly, 72-hr-oldbiofilms treated with Mg(OH)₂ nanoplatelets exhibited more decline inbiofilm viability than 120-hr-old films. At 120 hr, Mg(OH)₂nanoplatelets were less effective and had almost no activity (FIG. 5B).These results show that the nanoplatelets possess high antibacterialactivity. Actually, their high specific surface area and porousstructure favor the nanoplatelets to show high antibacterial activity.That is why they can be useful to preserve materials in glasscontainers.

Catalytic Application

Reduction of 4-NP was chosen as a model reaction to investigate thecatalytic activity of Mg(OH)₂ nanoplatelets. 4-NP is commonly present inindustrial waste water because it is used in pharmaceutical and textileindustries and in organic synthesis [A. Chwalibog, E. Sawosz, A. Hotowy,J. Szeliga, S. Mitura, K. Mitura, M. Grodzik, P. Orlowski, A.Sokolowska, Int. J. Nanomed. 2010, 5, 1085]. 4-NP is converted into4-aminophenol (4-AP) through reduction with the help of a reducingagent. 4-AP is much less dangerous than 4-NP. Moreover, 4-AP is used inthe polymer industry. Thus this reaction is very importantenvironmentally as well as economically. The nanoplatelets can increasethe speed of reaction many times. Thus, the product is formed in ashorter period of time. Here, the catalytic reduction of 4-NP wasmonitored with the help of UV-visible spectrophotometry because 4-NPstrongly absorbs at 400 nm in a basic medium [X. Le, Z. Dong, X. Li, W.

Zhang, M. Le, J. Ma, Catal. Commun. 2015, 59, 21]. The concentration ofNaBH4 is kept 100 times (or more) greater than that of 4-NP, so thecatalytic reduction obeys pseudo-first-order kinetics. Plot of ln(At/Ao)as a function of time for catalysis is shown in FIG. 6A. In this plot,the value of ln(At/Ao) decreases with time. This shows that catalysis isin progress and 4-NP is rapidly being converted into 4-AP. After 4 min,the value of ln(At/Ao) becomes constant, which shows that the catalysishas completed. Apparent rate constant (kapp) was calculated from theslope of this graph, which was found to be 0.0067 and 0.0072/min at 60and 70 mg/L catalyst dosages. These values of kapp are greater thanthose of many other reported catalysts under the same conditions [M.Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, M. Bagherzadeh,R.Safari, J. Mol. Catal. A 2015, 400, 22; and S. Gu, J. Kaiser, G. Marzun,A. Ott, Y. Lu, M. Ballauff, A. Zaccone,S. Barcikowski, P. Wagener,Catal. Lett. 2015, 145, 1105.]. The greater value of kapp is due to thehigh specific surface area and porous structure of the nanoplatelets.The value of kapp for 70 mg/L is found to be greater than that of 60mg/L catalyst dosage. The number of surface sites for catalysis hasincreased with the increase in catalyst dosage. That is why the value ofkapp at 70 mg/L is greater than that at 60 mg/L. Reusability of thecatalyst was also investigated up to five cycles of usage (FIG. 6B). Itwas found that the catalytic activity decreased by only 6% after fourrecycles. It means that the nanoplatelets can be successfully used againand again.

EXPERIMENTAL

Materials

Magnesium chloride (MgCl₂), sodium acetate (CH₃COON_(a)), ethyleneglycol, and dimethylsulfoxide (DMSO) were purchased from Sigma-Aldrich(USA). All chemicals were used as received without any furtherpurification. Three isolated and ribotyped antibiotic-resistant strains,E. coli (kt273995), K. pneumoniae (kt273996), S. aureus (kt250728), wereobtained from the Department of Microbiology and Molecular genetics,University of the Punjab, Lahore, Pakistan. The bacterial culture wasmaintained in Luria-Bertani (LB) broth and agar purchased from Merck(Germany).

Synthesis of Magnesium Hydroxide Nanoplatelets

Mg(OH)₂ nanoplatelets were produced by the solvothermal method. Twentymilliliters of 1 M CH₃COON_(a) solution was dropwise added into 20 mL of0.5 M MgCl₂ solution. The reaction mixture was stirred for 15 min atroom temperature. Then 10 mL of ethylene glycol was added into it andreaction mixture was further stirred for 15 min. Then reaction mixturewas heated at 180° C. for 8 hr in an autoclave solvothermal reactor. Thewhite precipitates formed were collected by centrifugation and thepellets were washed thrice with deionized water and thrice withmethanol. The obtained white product was dried overnight at 60° C. undervacuum.

Applications of Magnesium Hydroxide Nanoplatelets

Antibacterial Application

The MIC and MBC of Mg(OH)₂ nanoplatelets against all the three strainswere evaluated by the broth-microdilution method [S. Gu, J. Kaiser, G.Marzun, A. Ott, Y. Lu, M. Ballauff, A. Zaccone, S. Barcikowski, P.Wagener, Catal. Lett. 2015, 145, 1105; and Z. Dong, X Le, C. Dong, W.Zhang, X. Li, J. Ma, Appl. Catal., B 2015, 162, 372]. Using 96-wellsmicroliter plates, 100 μL of Mg(OH)₂ nanoplatelet suspension (2,000μg/mL) was dispensed into well 1 and serially diluted across the plateup to well 10. Then 100 μL of LB broth and 100 μL of 5×105 CFU/mLbacterial inoculum were added into wells 1-12, leaving well 11 empty forsterile control, and incubated at 37° C. for 18-24 hr. The redox dye NBT(0.2 mg/mL) was used to detect the bacterial growth by the color changefrom yellow to blue. After 24 hr, the absorbance of each plate wasmeasured at 630 nm by a microplate reader. All MIC measurements werecarried out in triplicate. MBC was determined by aspirating 100 μL ofthe culture medium from the wells (at MIC and above MIC) and subculturing it on fresh LB agar followed by incubation at 37° C. for 24-48hr. Antibacterial activity of various concentrations of Mg(OH)₂nanoplatelets against all three bacterial strains was examined by thewell diffusion method. Absolute methanol was used as negative control.The inoculum suspension of 0.5 McFarland standard of each bacterialstrain was subcultured on the surface of LB agar plates. Wells of 5 mmdiameter were made aseptically on the LB plates. One hundred microlitersof various concentrations of Mg(OH)₂ nanoplatelets (3,000, 2,000, and1,000 μg/mL) was dispensed into separate wells and the plates wereincubated at 37° C. for 24 hr. The antimicrobial susceptibility wasexamined by measuring the diameter of the zones of inhibition expressedin millimeters against the tested strains. To investigate theantibiofilm activity of the nanoplatelets, 0.1 mL of bacterial culture(1.5×108 CFU/mL) and 0.1 mL of LB broth containing Mg(OH)₂ nanoplatelets(subinhibitory concentration, 0.5×MIC) were transferred into 96-wellmicrotiter plates. Then microtiter plates were incubated aerobically for48, 72, 96, and 120 hr at 37° C. After 48, 72, 96, and 120 hr, thegrowth medium was disposed of and the microtiter plate wells were washedtwice with 200 NL normal saline to remove nonadherent cells andsubsequently air-dried in an inverted position for 30 min. The adherentbiofilm was fixed with 95% ethanol and was stained with 200 μL of 1 v/v% CV for 20 min at room temperature. Overabundant dye was expelled bywashing each well thrice with 200 μL of sterile normal saline.Quantification of the attached cells was done by adding 200 μL ofglacial acetic acid (33 v/v %) as a CV dissolvable to elute the stainedcells. Thereafter, the absorbance at 546 nm wavelength of dissolved CVwas measured using a microplate reader (BioRad, MicroplateReader-680XR). The experiment was performed in triplicate, and sterileLB broth containing Mg(OH)₂ nanoplatelets was utilized as negativecontrol while LB broth containing bacterial strains was utilized aspositive control. The same protocol was used to study the effect ofMg(OH)₂ nanoplatelet activity on established biofilm on a 96-wellmicrotiter plate.

Catalytic Application

Twenty microliters of 0.1 mM 4-NP, 8 mL of 25 mM NaBH4, 64 mL deionizedwater, and 8 mL of catalyst dispersion were added into a cuvette. Then,absorbance at 400 nm (A max of 4-NP at pH≥9) was measured after every 15s on a UVD-3500 spectrophotometer. Absorbance was measured until itbecame constant. The kinetics of catalysis was studied using theequation ln(At/A0)=−kapp×t, where AO and At are the absorbance at 400 nmat 0 time and time 1, respectively. kapp is the apparent rate constantof catalysis.

Characterization

XRD patterns were obtained on a Rigaku D/max Ultima III Xraydiffractometer with a Cu Kα radiation source (λ=0.15406 nm) operated at40 kV and 150 mA and at scanning steps of 0.02° in the 20 range 10-60°.TEM observations were carried out on an FEI Tecnai G2 S-Twintransmission electron microscope with an accelerating voltage of 200 kV.A twin surface area analyzer (Quantachrome Instruments, USA) was used tomeasure the surface area of the product using nitrogen at −196° C.temperature and degassing at 200° C. for 1 hr. The specific surface areaof the samples was calculated using the BET method, and the BJH modelwas applied to the pore size distributions derived from the desorptionbranches of the isotherms. Catalytic activity was monitored using aUVD3500 spectrophotometer (Laboomed, Inc., USA).

The invention claimed is:
 1. A method for making mesoporous magnesiumhydroxide nanoplates with a diameter of 20 nm to 100 nm and a thicknessof 0.5 to 30 nm, the method comprising: heating an aqueous mixture of amagnesium salt, a base, and a glycol having 2 to 6 carbon atoms at atemperature of 140 to 220′C for 1 to 24 hours, wherein the aqueousmixture is substantially free of a surfactant, a template, or both, andwherein the heating forms a precipitate containing the mesoporousmagnesium hydroxide nanoplates; wherein the mesoporous magnesiumhydroxide nanoplates are hollow having a thin-walled shell surroundingan interior void; wherein the thin-walled shell has a thickness of0.1-10 nm; wherein the mesoporous magnesium hydroxide nanoplates are notagglomerated.
 2. The method of claim 1, wherein the magnesium salt is amagnesium halide.
 3. The method of claim 2, wherein the magnesium halideis magnesium chloride.
 4. The method of claim 1, wherein the magnesiumsalt is present in the aqueous mixture in an amount of 15 to 25 g/L. 5.The method of claim 1, wherein the base is a monoacidic base.
 6. Themethod of claim 1, wherein the base is an acetate base.
 7. The method ofclaim 1, wherein the base is sodium acetate.
 8. The method of claim 1,wherein the base is present in the aqueous mixture in an amount of 25 to40 g/L.
 9. The method of claim 1, wherein a mole ratio of the amount ofbase present in the aqueous mixture to the amount of magnesium presentin the aqueous mixture is 1:1 to 3:1.
 10. The method of claim 1, whereinthe glycol is ethylene glycol.
 11. The method of claim 1, wherein theglycol is present in the aqueous mixture in an amount of to 25 volume %,based on a total volume of the aqueous mixture.
 12. The method of claim1, wherein the aqueous mixture is formed by mixing the magnesium saltand the base in water for 1 to 30 minutes, followed by the addition ofthe glycol.
 13. The method of claim 12, wherein after the addition ofthe glycol, the aqueous mixture is mixed for 1 to 30 minutes before theheating.
 14. The method of claim 1, wherein the mesoporous magnesiumhydroxide nanoplates have a mean pore diameter of 2 to 10 nm, a surfacearea of 50 to 70 m²/g, and a type-III nitrogen adsorption-desorption BETisotherm with a H3 hysteresis loop.
 15. The method of claim 1, whereinthe mesoporous magnesium hydroxide nanoplates have a multimodal sizedistribution.